<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <title>Document</title>

    <style>
        .outer {
            width: 200px;
            height: 200px;
            border: 2px solid black;
            margin: 0 auto;
            margin-top: 100px;
        }

        .inner {
            width: 200px;
            height: 200px;
            background-color: deepskyblue;
            transform: rotateZ(45deg);
        }
    </style>
</head>
<body>

    <div class="outer">
        <div class="inner">你好啊</div>

    </div>
    
</body>
</html>